Morphology-Tuned Phase Transitions of Anatase TiO₂ Nanowires under High Pressure

Abstract

The phase transitions of one-dimensional (1D) anatase TiO2 nanowires were studied by in situ high-pressure synchrotron X-ray diffraction and Raman scattering up to 37 GPa. A direct anatase-to-baddeleyite transformation was observed at ∼9 GPa, which is clearly different from the size-dependent phase transition behaviors for nanocrystalline TiO2. We found the higher compressibility in the c-axis compared to the a-axis for anatase nanowires that may be attributed to both the crystal structural feature and the growth direction of the nanowires. The Ti–O bonds show abnormal changes during the anatase-to-baddeleyite phase transition. This phase transition of the TiO2 nanowires shows obvious morphology-tuned behaviors. Upon decompression, the baddeleyite phase transformed into α-PbO2 phase. The morphology of the TiO2 nanowires shows excellent stability and TiO2 nanowires with α-PbO2 phase were obtained at ambient conditions through a compression–decompression cycle. These results indicate that the nanoscale quasi-1D structure of TiO2 nanowires may contribute to the high-pressure phase transitions showing unique morphology-tuned behaviors.